This invention relates generally to refrigeration and, more particularly, to refrigeration for superconductivity applications.
Superconductivity is the phenomenon wherein certain metals, alloys and compounds lose electrical resistance so that they have infinite electrical conductivity. Until recently, superconductivity was observed only at extremely low temperatures just slightly above absolute zero. Maintaining superconductors at such low temperatures is very expensive, typically requiring the use of liquid helium, thus limiting the commercial applications for this technology.
Recently a number of materials have been discovered which exhibit superconductivity at higher temperatures, such as in the range from 15 to 75 K. Liquid nitrogen, a relatively low cost way to provide cryogenic refrigeration, cannot effectively provide refrigeration to get down to the superconducting temperatures of most high temperature superconductors.
An electric transmission cable made of high temperature superconducting materials offers significant benefits for the transmission of large amounts of electricity with very little loss. High temperature superconducting material performance generally improves roughly an order of magnitude at temperatures of about 30 to 40 K from that at temperatures around 80 K which is achieved using liquid nitrogen.
The application of superconducting equipment such as motors, transformers, generators, magnets and others is dependent in part on the development of reliable refrigeration systems. Superconducting systems need to be maintained at temperatures in the range of 4 to 80 K and to be shielded from heat leak starting at ambient temperature down to the operating temperature of the superconducting system.
Accordingly, it is an object of this invention to provide an effective and reliable system for providing refrigeration to superconducting equipment.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure are attained by the present invention, one aspect of which is:
A method for providing refrigeration to superconducting equipment comprising:
(A) providing refrigeration from a cryocooler to a cooling fluid to produce cooled cooling fluid;
(B) warming the cooled cooling fluid by indirect heat exchange with ballast liquid; and thereafter
(C) passing the cooling fluid to superconducting equipment and providing refrigeration to the superconducting equipment.
Another aspect of the invention is:
Apparatus for providing refrigeration to superconducting equipment comprising:
(A) a cryocooler and means for passing cooling fluid to the cryocooler;
(B) a ballast tank containing ballast liquid, and means for passing cooling fluid from the cryocooler in indirect heat exchange with the ballast liquid within the ballast tank; and
(C) superconducting equipment, and means for passing cooling fluid from the ballast tank to the superconducting equipment.
As used herein the term xe2x80x9ccryogenic temperaturexe2x80x9d means a temperature at or below 120 K.
As used herein the term xe2x80x9ccrycoolerxe2x80x9d means a refrigerating machine able to achieve and maintain cryogenic temperatures
As used herein the term xe2x80x9csuperconductorxe2x80x9d means a material that loses all of its resistance to the conduction of an electrical current once the material attains some cryogenic temperature.
As used herein the term xe2x80x9crefrigerationxe2x80x9d means the capability to reject heat from a subambient temperature entity.
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cdirect heat exchangexe2x80x9d means the transfer of refrigeration through contact of cooling and heating entities.
As used herein the term xe2x80x9csuperconducting equipmentxe2x80x9d means equipment that utilizes superconductor material, for example, in the form of wire for the coils of a rotor for a generator or motor, or for the coils of a magnet or transformer.